The low-permeability reservoir has poor physical properties, complex pore structure, low surface porosity and small throat, and therefore, an expected yield-increasing effect is hardly achieved by a conventional fracturing technology. The volume fracturing technology is an important technological measure to reform a low-permeability oil/gas field and increase the yield. Horizontal well volume fracturing is the main technical means for yield increase and reformation a low-permeability oil/gas reservoir. However, low-permeability oil/gas reservoirs in China are dominated by continental deposits, and low-permeability reservoirs developed in some oilfield blocks (such as some blocks in the Changqing Oilfield and Jilin Oilfield) are characterized by small reservoir forming areas, more longitudinal sublayers and small thickness. Therefore, the horizontal well volume reform technology shows some inadaptability, making the vertical well volume fracturing technology applied to the development of such reservoirs on a large scale. Accurate interpretation results of fractured reservoir reform volume are conducive to reasonably evaluating the vertical well volume fracturing effect, optimizing the fracturing construction design and accurately predicting the yield after fracturing. At present, the commonly used methods for on-site monitoring of a volume fractured fracture at home and abroad include micro-seismic monitoring, inclinometer monitoring, and distributed acoustic sensing fracture monitoring. The micro-seismic monitoring which is a widely used fracture monitoring method can be used to detect the orientation, fracture length, fracture width, fracture height and inclination angle of a complex fracture network body. However, this method has high technical cost and is not suitable for large-scale multi-well applications. If a reservoir reform volume mathematical model is used to predict the reservoir reform volume after volume fracturing, the cost can be greatly reduced. The existing reservoir reform volume prediction methods mainly include a semi-analysis method, a yield fitting method and a discrete fracture network simulation method. The semi-analysis method and the yield fitting method have higher requirements for basic data, so the former needs micro-seismic monitoring data of part of wells in the target block for performing calibration to obtain reliable prediction results, while the latter is necessary to predict the magnitude of the reservoir reform volume based on yield data after fracturing. Although a discrete fracture network simulation method does not need to obtain the micro-seismic monitoring data and the yield data after fracturing in advance, but is relatively complex in basic theories, large in calculation amount, poor in model convergence and not easy to implement. Therefore, it can be seen that the existing method for predicting the reservoir reform volume has certain deficiencies and is thus not suitable for large-scale application field practice.
To sum up, the currently required method for predicting a reservoir reform volume after vertical well volume fracturing of a low-permeability oil/gas reservoir should have the following two characteristics: (1) the requirements for basic data are relatively low during implementation, and the reservoir reform volume after volume fracturing can be directly predicted without the need to obtain a large amount of basic data such as micro-seismic monitoring data and yield data after fracturing in advance; (2) the basic theory is perfect, the idea is concise and intuitive, the operability is high, and accurate prediction results can be obtained.